1. Technical Field
The present invention relates to wireless communication and, in particular, to a method of determining a transmit power on an uplink channel in a wireless communication system such as a general packet radio service (GPRS) system.
2. Related Art
The GSM (Global System for Mobile communication) is a radio technology which has been developed as a system for standardizing radio communication systems in Europe and which has widely been deployed all over the world. The GPRS (General Packet Radio Service) is introduced to provide a packet switched data service in a circuit switched data service provided from the GSM. The EDGE (Enhanced Data Rate for GSM Evolution) employs the 8-PSK (Phase Shift Keying) instead of the GMSK (Gaussian Minimum Shift Keying) employed in the GSM. The EGPRS (Enhanced General Packet Radio Service) represents the GPRS using the EDGE.
The physical channel dedicated to GPRS/EGPRS traffic is called Packet Data Channel (PDCH). Logical channels such as Packet Common Control Channel (PCCCH), Packet Data Traffic Channel (PDTCH) and Packet Associated Control Channel (PACCH) are mapped to the PDCH. The PCCCH is used for control signaling necessary for initiating packet transfer. The PDTCH is used to transmit user data. The PACCH is used for dedicated signaling.
Time division multiplex access (TDMA) scheme is applied in GSM/GPRS/EDGE systems. In TDMA scheme, each mobile station in a cell transmits and receives circuit switched data and/or packet switched data through assigned timeslots. One to eight timeslots can be allocated to a mobile station per TDMA frame. Timeslots are shared by the active users, and uplink and downlink timeslots are allocated separately. Hereinafter, downlink means communication from a network to a mobile station, and uplink means communication from a mobile station to a network. In GPRS/EDGE system, users can share a single timeslot simultaneously with several users in a cell. A single user may transmit and receive data over multiple timeslots simultaneously.
The power control is necessary to mitigate co-channel interference in a wireless communication system. Keeping co-channel interference levels low can result in higher throughput over a cell, potentially increasing cell's capacity. Effective power control ensures that timeslots used for GSM/GPRS/EDGE system do not cause unacceptable levels of interference to timeslots used for voice calls in co-channel neighbor cells.
Inadequate power control can cause high error rates or, at worst, broken radio connections which in known as temporary block flows (TBFs). Power control errors may increase packet delays and decrease user throughputs, thus causing service degradation.
Uplink power control mechanisms allow a network to tune uplink transmit power used by each mobile station transmitting uplink data blocks. Uplink power control provides an additional important benefit: transmit power used by each mobile station can be reduced to levels adequate to achieve proper link performance and transmit power can be kept as low as possible without sacrificing link throughput, giving users peak link performance without unnecessarily draining the mobile station's battery.